Sunday, June 28, 2009

Every summer since 2003, emails make the rounds talking about how Mars will appear as big as the full Moon. This is complete nonsense.

I received my first Mars Hoax email of the season last week and thought I should clear the air.

In fact not only is Mars not going to be this big, in one sense it is shrinking ...

Origins of the Mars Hoax

On August 27, 2003 Mars and Earth lined up in what is known as an inferior conjunction or opposition. This is a normal astronomical event which happens every 26 months. That year the opposition was special because it was closer than normal. A lot was made of the fact that at 55.7 million km it was the closest Mars and Earth had come in almost 60,000 years.

A more realistic view is that Mars and Earth oppositions bring the two planets within the wide range of 55 to 101 million km. But they only get to close end of this range every 7 or 8 oppositions (e.g. 1956, 1971, 1988, 2003, 2018, 2035, 2050). When Mars is in close opposition it is nearly twice as close and will appear nearly twice as big. During these close oppositions Mars will appear much brighter than normal but you will still need a telescope to see it. These close oppositions are the very best times to see Mars through a telescope. The neighbouring oppositions (e.g. 2001, 2005, 2016, 2020) also allow excellent viewing opportunities.

Last December the two planets were on opposite sides of the Sun and almost 400 million km apart. The next oppositions in 2010, 2012, and 2014 are among the farthest and least interesting. So when the Mars Hoax email comes around in one of these poor years - enjoy a chuckle. Mars will continue to appear smaller and smaller until after 2012 when it begins to return to its regularly scheduled close oppositions. So in that sense, Mars is shrinking.

Click here for tables of Mars oppositions and closest approaches and a technical explanation at SEDS (Students for the Exploration and Discovery of Space).

Want to See for yourself?

Nothing helps like a visual. Try out the NASA/JPL orbit simulator, here. The reason I've used the asteroid Ceres to trick the simulator because you can't look up a planet or a moon in its database. Now you should:

Click the Orbits drop down and select in order: No Orbits, Earth, and Mars

Turn off the Distance label

Zoom in a bit to get Ceres out of the picture

Set the Way-back machine to Aug 27th 2003 (use Date or just run it backwards using "<<")

Rotate the frame so Earth and Mars are front and center

Set the Interval beside the date to 1 year

Step forward and back

What Others are Saying?

A quick search of Google for Mars+Hoax gets 810,000 hits. There are pages on the Mars Hoax at both Wikipedia and Snopes.com. Here are what just a few knowledgeable people are saying about this hoax:

The diameters of Mars and our Moon are about 6752 km to 3470 km or just about 2 to 1. For Mars to appear the same size as our Moon it would need to be much closer to us. About twice as far as our Moon in fact. At that distance Mars would be inside the Earth’s Hill Sphere and we would either have a second moon or be in really big trouble (see the picture above).

On a Lighter Note

Planetary oppositions of Mars were featured in two Warner Brothers cartoons:

"Rocket-Bye Baby" used a close approach to Mars in 1954 to set up a cosmic mix up where a Martian and human baby were switched.